Doolandella Ground Gas Monitoring

When concern was raised over potentially hazardous ground gases from a former landfill adjoining a new estate for low density housing, Douglas Partners was called upon to investigate and assist the site owner to comply with relevant health, safety and environmental regulations.

A new estate for low density housing was proposed to be developed adjoining the former Willawong landfill at Doolandella, near Forest Lake, and potential existed for hazardous ground gases from the landfill including methane, hydrogen sulphide, carbon monoxide and carbon dioxide to impact on the development. An investigation was required by Brisbane City Council to identify any ground gases along the boundaries of the development site that adjoined the former landfill.

 Douglas Partners was retained by the developer for the investigation, and this comprised installation of a number of gas collection wells approximately   four metres in depth below ground, and monitoring for gases in the wells over several events. The project was conducted in accordance with the NSW EPA 2012 guidelines for assessment of hazardous ground gases, where both the concentration and flow rate of gases were measured in each well. From these data, “Gas Screening Values” were calculated to identify the risk factor and any remediation requirement.

 Douglas Partners was pleased to assist the site owner to comply with the relevant health, safety and environmental regulations, and ensure that the development could be constructed without any potential for impact from hazardous ground gases.

Findings from the investigation improved the site classification from that previously recommended by others and allowed the Project Civil Engineers to optimise earthworks to achieve a combination of Class A and Class S lots. In addition to the original scope of works, Douglas Partners was engaged to return to the site and undertake a detailed investigation of a seasonally waterlogged part of the site. The detailed investigation identified an irregular zone of low permeability material at the interface of two major geological units causing the westerly flowing groundwater to become trapped, or ‘dammed’ and forced to intersect the ground surfaces in winter months. The model of the underground feature was provided to the civil engineers with recommendations on strategies to manage the groundwater with respect to the proposed development.

Douglas Partners’ assistance was also requested to maximise the efficiency of the earthworks, providing advice on alternative filling materials, confirming adequacy of the results of the earthworks and confirming final site classification.